In the search for petroleum and other valuable resources, it has become the practice to transmit a seismic signal into the earth from one or more source points near the surface of the earth. The reflected and/or refracted energy returning from within the earth to a receiver location is detected by a geophone or other seismometer and raw seismic data are recorded. The raw seismic data are mathematically processed and then interpreted to provide an indication of the structure of the underlying strata.
Geophones are disposed in accordance with the requirements of a particular survey at spaced intervals for reception of seismic source signals as they arrive through the air, directly from the source or sources along the surface of the ground and as refracted and reflected by the lithological character of the subsurface. The received data in the form of acoustical energy or elastic motion is converted to corresponding electrical signals by the element or elements in each geophone for transmission and recording with related data from the sources and from other geophones. Finally, the data is processed and interpreted or analyzed to yield information about the subsurface character of the lithology. Typically, this is done to determine if there might by hydrocarbon deposits and, if so, at what depths and in what quantity.
Although surveys vary tremendously in their requirements, it is not uncommon for a particular survey to require dozens of geophones. Further, after the readings are recorded for a first location, the geophones are located for taking numerous subsequent readings.
Seismic acquisition systems today oftentimes utilize time as a factor in so called "4-d" seismic acquisition for ascertaining any movement of petrolites or hydrocarbons. In such a seismic acquisition, the same spread configuration of the geophones buried in the earth is surveyed at different time intervals. Two or more surveys at time intervals of several months or a few years are made in order to ascertain any migration of hydrocarbons. For such surveys, it is extremely critical for accurate results that the positioning of the geophones and energy sources are at or very near the same position each time data is acquired by a survey. It is very difficult to position the geophones at the same location if the geophones are removed after each survey particularly when several months or years occur between subsequent surveys.
It is an object of the present invention to provide a seismic acquisition system for multiple surveys or shoots separated by predetermined time intervals and utilizing geophones which are positioned in the same position for all of the surveys.
A further object of the invention is to provide a geophone storage structure buried in the earth for storing a geophone therein so that the geophone may be utilized at a fixed earth position for multiple surveys taken over long time periods.